Script day: output the tail of a log based on time

As system administrators we often want to list the last few lines from a log file in order to track problems and see system reports. The UNIX command tail is very useful for that purpose and lets you display an arbitrary number of lines from the bottom of any file.

But often this is not really what you want – an administrator might want to see what happens in the last X minutes and the common practice to do this is to run tail with a guessed number of lines, see if you get what you want and if its not enough increase the number and try again.

Here’s another approach that works well if the log file you want to trace has time stamps for its lines (more…)

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How to build a chroot jail environment for CentOS

A chroot environment is simply a directory – inside which you can find a file system hierarchy exactly like your original operating system. You can then use the UNIX chroot command to open a shell in that directory so that command running under that shell see only the chroot environment and can’t mess up your system. This is very useful for many different reasons – for example if you want to build some software packages and you don’t want their build dependencies to pollute your real system.

Building a chroot environment is not difficult at all using the right tools, and YUM – the CentOS installation tool – has what you need.

(more…)

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